linux-kernel - Re: [tip:perf/core] x86, tracing, perf: Add trace point for MSR accesses

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Date:	Fri, 4 Dec 2015 13:11:15 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-tip-commits@...r.kernel.org, vincent.weaver@...ne.edu,
	eranian@...gle.com, hpa@...or.com, efault@....de,
	peterz@...radead.org, jolsa@...hat.com,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	ak@...ux.intel.com, rostedt@...dmis.org, acme@...hat.com,
	mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [tip:perf/core] x86, tracing, perf: Add trace point for MSR
 accesses

On Fri, Dec 04, 2015 at 03:59:42AM -0800, tip-bot for Andi Kleen wrote:
> Commit-ID:  07b41f5cf37b34ef3de4f40fbaf8547abe690abb
> Gitweb:     http://git.kernel.org/tip/07b41f5cf37b34ef3de4f40fbaf8547abe690abb
> Author:     Andi Kleen <ak@...ux.intel.com>
> AuthorDate: Tue, 1 Dec 2015 17:00:59 -0800
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Fri, 4 Dec 2015 10:58:34 +0100
> 
> x86, tracing, perf: Add trace point for MSR accesses
> 
> For debugging low level code interacting with the CPU it is often
> useful to trace the MSR read/writes. This gives a concise summary of
> PMU and other operations.
> 
> perf has an ad-hoc way to do this using trace_printk, but it's
> somewhat limited (and also now spews ugly boot messages when enabled)
> 
> Instead define real trace points for all MSR accesses.
> 
> This adds three new trace points: read_msr and write_msr and rdpmc.
> 
> They also report if the access faulted (if *_safe is used)
> 
> This allows filtering and triggering on specific MSR values, which
> allows various more advanced debugging techniques.
> 
> All the values are well defined in the CPU documentation.
> 
> The trace can be post processed with
> Documentation/trace/postprocess/decode_msr.py to add symbolic MSR
> names to the trace.
> 
> I only added it to native MSR accesses in C, not paravirtualized or in
> entry*.S (which is not too interesting)
> 
> Originally the patch kit moved the MSRs out of line.  This uses an
> alternative approach recommended by Steven Rostedt of only moving the
> trace calls out of line, but open coding the access to the jump label.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Steven Rostedt <rostedt@...dmis.org>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Mike Galbraith <efault@....de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Stephane Eranian <eranian@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Vince Weaver <vincent.weaver@...ne.edu>
> Link: http://lkml.kernel.org/r/1449018060-1742-3-git-send-email-andi@firstfloor.org
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---

...

> diff --git a/arch/x86/lib/msr.c b/arch/x86/lib/msr.c
> index 4362373..004c861 100644
> --- a/arch/x86/lib/msr.c
> +++ b/arch/x86/lib/msr.c
> @@ -1,6 +1,8 @@
>  #include <linux/module.h>
>  #include <linux/preempt.h>
>  #include <asm/msr.h>
> +#define CREATE_TRACE_POINTS
> +#include <asm/msr-trace.h>
>  
>  struct msr *msrs_alloc(void)
>  {
> @@ -108,3 +110,27 @@ int msr_clear_bit(u32 msr, u8 bit)
>  {
>  	return __flip_bit(msr, bit, false);
>  }
> +
> +#ifdef CONFIG_TRACEPOINTS
> +void do_trace_write_msr(unsigned msr, u64 val, int failed)
> +{
> +	trace_write_msr(msr, val, failed);
> +}
> +EXPORT_SYMBOL(do_trace_write_msr);
> +EXPORT_TRACEPOINT_SYMBOL(write_msr);
> +
> +void do_trace_read_msr(unsigned msr, u64 val, int failed)
> +{
> +	trace_read_msr(msr, val, failed);
> +}
> +EXPORT_SYMBOL(do_trace_read_msr);
> +EXPORT_TRACEPOINT_SYMBOL(read_msr);
> +
> +void do_trace_rdpmc(unsigned counter, u64 val, int failed)
> +{
> +	trace_rdpmc(counter, val, failed);
> +}
> +EXPORT_SYMBOL(do_trace_rdpmc);
> +EXPORT_TRACEPOINT_SYMBOL(rdpmc);

Any particular reason why those are EXPORT_SYMBOL and not
EXPORT_SYMBOL_GPL?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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